Hi Renyue,

It depends a bit on how you are saving the image, unfortunately.  If you are using a recent changeset of yt (after 2.4 where the transpose causes symmetric images on some compilers/machines), and you save with:

cam.snapshot('image1.png')

Then image1.png will have north pointing up.

If you did:

im = cam.snapshot()

write_bitmap(im, 'image2.png', tranpose=False)

Then image2.png will have north pointing right.

If you did 

im = cam.snapshot()

write_bitmap(im, 'image3.png', transpose=True)

Then image3.png will have north pointing up.

I am working on ways to make sure that it always points up by using the new ImageArray class, but have not come up with the full solution yet.  I hope that description helps.

Sam

On Sat, Jan 12, 2013 at 8:12 PM, Renyue Cen <cen@astro.princeton.edu> wrote:

Hi,

I think I am unclear about the orientation in pf.h.camera(c,W,L, ..., north=vec, ...).
I  got some nice looking pictures but don't know what north means in this case,
because when I switch north=vec to north=reverse of vec, the image rotates along the vertical direction,
so it seems like north is pointing to either left or right.  It is very desirable for me to be able
to make sure which direction vec points to (vec is the vec in north=vec) in the final rendered plot.


Thanks in advance for help,
Renyue